Philip Hodge

Terminology for biorelated polymers and applications (IUPAC Recommendations 2012)

Like most of the materials used by humans, polymeric materials are proposed in the literature and occasionally exploited clinically, as such, as devices or as part of devices, by surgeons, dentists, and pharmacists to treat traumata and diseases. Applications have in common the fact that polymers function in contact with animal and human cells, tissues, and/or organs. More recently, people have realized that polymers that are used as plastics in packaging, as colloidal suspension in paints, and under many other forms in the environment, are also in contact with living systems and raise problems related to sustainability, delivery of chemicals or pollutants, and elimination of wastes. These problems are basically comparable to those found in therapy. Last but not least, biotechnology and renewable resources are regarded as attractive sources of polymers. In all cases, water, ions, biopolymers, cells, and tissues are involved. Polymer scientists, therapists, biologists, and ecologists should thus use the same terminology to reflect similar properties, phenomena, and mechanisms. Of particular interest is the domain of the so-called “degradable or biodegradable polymers” that are aimed at providing materials with specific time-limited applications in medicine and in the environment where the respect of living systems, the elimination, and/or the bio-recycling are mandatory, at least ideally.

Recent research on the synthesis and applications of cyclic oligomers

Cyclic oligomers may serve as starting materials for entropically-driven ring-opening polymerisations, as macrocyclic recognition systems and as building blocks for various novel structures. This has prompted the development of methods for synthesising cyclic oligomers. These include high-dilution methods, cyclo-depolymerisations and polymer-supported cyclo-oligomerisations. Recent progress in these areas is briefly reviewed and is illustrated with specific examples.

Synthesis and properties of low-molar-mass liquid-crystalline siloxane derivatives

A number of liquid-crystalline siloxane derivatives based on the 4-(ω-alkenyloxy)-4′-cyanobiphenyl mesogenic unit have been prepared and their phase-transitional properties characterised. The compounds were synthesized by the addition of the 4-(ω-alkenyloxy)-4′-cyanobiphenyl moiety to pentamethyldisiloxane catalysed by a platinum divinyltetramethyldisiloxane complex. The materials are denoted ABs where A refers to the number of methylene groups in the 4-(ω-alkenyloxy)-4′-cyanobiphenyl and B refers to the number of silicon atoms in the siloxane unit. With the exception of 3/2 and 4/2, which exhibit only monotropic phase transitions, all these materials exhibit an enantiotropic smectic A phase. Preliminary X-ray results also support this. The thermal properties of this new series of thermotropic liquid-crystalline siloxanes were studied by differential scanning calorimetry (DSC) and polarising microscopy. The transitional properties for the AB series exhibit a pronounced odd–even effect with the length of the alkyl segment.

NEW LOW MOLAR-MASS ORGANOSILOXANES WITH UNUSUAL FERROELECTRIC PROPERTIES

Abstract A new low molar mass chiral organosiloxane mesogen and its racemic analogue have been synthesized and their mesomorphic and ferroelectric properties investigated. The chiral derivative, denoted A∗B, exhibits one tilted enantiotropic ferroelectric smectic C mesophase over a broad temperature range, with very high tilt angles and moderate spontaneous polarization (36° and 19 nC cm−2 at 20°C). The achiral siloxane derivative, denoted A∗B, exhibits one broad enantiotropic smectic C phase. Preliminary electro-optic measurements indicate that the spontaneous polarization is weakly dependent on temperature between 10°C and 50°C, the latter being the S∗c to isotropic phase transition. The tilt angle and layer spacing are temperature independent, and current response times of less than 200 μs were measured at 25°C for fields of 10 V μ−1. These results are discussed in comparison with those for side chain polymer liquid crystal structures and other low molar mass ferroelectric materials.

Michael reactions carried out using a bench-top flow system

The Michael reaction between methyl 1-oxoindan-2-carboxylate and methyl vinyl ketone was achieved successfully by pumping solutions of the reactants in toluene through a fluid bed of Amberlyst A21 at 50 degrees C. The use of a fluid bed reactor is attractive as it allows gel-type beads, i.e. the type of bead used in most studies of polymer-supported (PS) organic reactions, to be used satisfactorily in a flow system. When polymer-supported cinchonidine was used in place of Amberlyst A21, the Michael product was obtained in high yield with an enantiomeric excess (ee) of 51%. This % ee is comparable to that achieved when the reaction was catalysed by cinchonidine itself.

Synthetic opals made by the Langmuir–Blodgett method

Monodispersive synthetic opal particles were formed by the method of Stober et al. [J. Colloid Interface Sci. 26 (1968) 62] and were made hydrophobic by reacting them with 3-(trimethoxysilyl)propyl methacrylate. Groups of particles were dissolved in chloroform and were spread at the air/water interface using a Nima trough. Each group studied consisted of particles, which had almost identical diameters. Isotherms were obtained and these are illustrated. The use of an optimum value of surface pressure and a high level of hydrophobicity made it possible to deposit good quality multilayers by the Langmuir–Blodgett method but we found that the Langmuir–Schaefer method was easier to use for less hydrophobic particles. The layers obtained were studied by scanning electron microscopy and we present the images obtained from these results.

Cyclic polyesters: 1. Preparation by a new synthetic method, using polymer-supported reagents

Abstract A new method of synthesizing cyclic polyesters is described, using polymer-supported reactions. This method involves the attachment of Ω-bromocarboxylate anions to the surface of an ion-exchange resin, followed by polymerization and cyclization by inter- and intramolecular alkylation reactions, respectively. The polymerization reaction results in the formation of oligomeric chain polyester molecules that remain bound to the resin by the carboxylate anion end group. The cyclization reaction results in the detachment of the cyclic product from the resin support. The cyclic polyester [(CH 2 ) 10 CO.O] x obtained was divided into a series of sharp fractions using preparative g.p.c. and each fraction was examined by analytical g.p.c. The cyclic nature of the polyester product was established by n.m.r. spectroscopy and by fast atom bombardment (f.a.b.) mass spectrometry. The f.a.b. mass spectrum of a fraction showed a series of spectral lines corresponding to [(CH 2 ) 10 CO.O] x with x = 2–7. The cyclic products were directly compared with analogous linear polymers.

Some applications of reactions which interconvert monomers, polymers and/or macrocycles

Various reactions which interconvert monomers, polymers and/or macrocycles are considered and, in most cases, recent examples presented. The reactions include step-growth polymerisations, high dilution syntheses of macrocyclic oligomers, entropically-driven ring-opening polymerisations of macrocyclic oligomers, cyclo-depolymerisations to afford cyclic oligomers, and equilibrations between cyclic oligomers to give soluble combinatorial libraries of macrocycles. The latter may be screened using a soluble functionalised polymer and high resolution diffusion ordered NMR spectroscopy.

Structural characterization of linear dimeric and cyclic tetrameric liquid crystalline siloxane derivatives

Abstract The phase behaviour and the structural characterization of a new series of linear dimeric and cyclic tetrameric molecules which contain three distinct parts, a cyanobiphenyl aromatic core (A), a paraffin chain (P) and a central siloxane group (B) with the A-P-B-P-A sequence, are described. Incompatible with one another, these parts tend to locate themselves in three separate sub-layers superposed in a partially bilayered smectic A structure. Each sub-layer adapts its internal structure in order to be appropriate for superposition, as in the case of organosiloxane molecules with the A-P-B sequence reported previously.

Synthesis of a series of cyclic oligo(alkylidene isophthalate)s by cyclo-depolymerisation

The synthesis of series of cyclic oligo(alkylidene isophthalate)s by the cyclo-depolymerisation of the corresponding linear polymers has been investigated and the yields of the various cyclic oligomers determined as a function of the polymer structure. With up to 15 ring atoms per repeat unit the main products are the cyclic dimers (up to 90% yield) with smaller amounts of the larger rings. When there are more than 16 ring atoms per repeat unit the main products are the cyclic monomers (up to 72% yield) with smaller amounts of the larger rings. Possible applications for such cyclic oligomers are discussed including their possible use as feedstocks for environmentally friendly entropically driven ring-opening polymerisations and as building blocks for novel polymeric structures.